This invention relates to recovering oil from an oil containing fluid mixture. In particular, this invention relates to such recovery at an oil handling facility located adjacent to a body of water, and to the disposal of the relatively oil-free fluid into the body of water.
In U.S. Pat. No. 3,893,918, issued July 8, 1975, there are disclosed skim piles or elongate separator conduits that are useful and efficient in such recovery and disposal operations. The length of the conduit and the operating procedures are such that the rising velocity of the oil in the mixture results in the establishment of an upper oil layer in the conduit.
One of the skim piles disclosed in that patent operates while in continuous communication with the body of water. As such, the total fluid level in the skim pile is responsive to changes in mean level of the water body. Provision is made for withdrawing oil from the oil layer on top of the total fluid column in response to sensing of the level of the interface between such oil layer and the remaining fluid column therebelow. In that fashion, one seeks to insure that only an oil rich mixture is withdrawn from the skim pile, rather than an oil-water mixture. Although that technique has proved quite acceptable, some difficulties have been encountered especially in situations where unpredictably large or erratic total fluid level changes are produced in response to changes in mean level of the body of water.
U.S. Pat. No. 3,893,918 also discloses a form of skim pile where the level of total fluid in the skim pile is basically isolated from changes in the mean level of the water body through use of a valve. Problems associated with changes in that mean water level are thereby avoided. Such skim piles are normally employed only in shallow water situations where the underwater extent of the skim pile, if it were open at the bottom, would not normally be great enough to allow for good separation of oil. This is because the terminal rising velocity of the oil would not sufficiently overcome the exit velocity of downward flow in the conduit. Although normally closed, valved, skim piles could be employed in deeper water situations, operational and maintenance difficulties could become prominent by reason of the need to control a valve positioned at great depth.
Another form of skim pile has accomplished isolation of the total fluid therein from changes in mean water level without problems associated with underwater valve operation. In that form of skim pile, a generally U-shaped conduit is connected at one end near the bottom of the skim pile, and the upper covered portion of the conduit extends well above the water line. The U-shaped conduit thus functions as a weir which essentially maintains a fixed, above-water level of total fluid in the skim pile, while isolating that fluid from level changes in the water body. However, use of such skim piles is not without its problems. The expense associated with construction of the weir leg can itself be quite considerable in deep water installations. Moreover, difficulties may be associated with removal of solid particles, such as sand, which settle out and collect at the bottom of the skim pile. A valve can be employed for periodic release of those collected particles, but, again, that creates the necessity for underwater valve operation and maintenance.
In U.S. Pat. No. 3,756,409, issued Sept. 4, 1973, there is proposed a separator conduit where an internal weir-like arrangement is employed, not for total fluid maintenance, but for collection, in a tube, of spillover oil which rises to the top of the fluid column in the conduit. Since that fluid column is responsive to changes in mean level of the body of water, it will be appreciated that spillover of substantial amounts of water into the collection tube could easily result, thereby considerably reducing the efficiency of operation.